add lock.yml

+# Configuration for Lock Threads - https://github.com/dessant/lock-threads-app
+
+# Number of days of inactivity before a closed issue or pull request is locked
+daysUntilLock: 14
+
+# Skip issues and pull requests created before a given timestamp. Timestamp must
+# follow ISO 8601 (`YYYY-MM-DD`). Set to `false` to disable
+skipCreatedBefore: false
+
+# Issues and pull requests with these labels will be ignored. Set to `[]` to disable
+exemptLabels: []
+
+# Label to add before locking, such as `outdated`. Set to `false` to disable
+lockLabel: false
+
+# Comment to post before locking. Set to `false` to disable
+lockComment: >
+  This thread has been automatically locked since there has not been
+  any recent activity after it was closed. If you are still experiencing a
+  similar issue, please open a new bug, including the output of
+  `flutter doctor -v` and a minimal reproduction of the issue.
+# Assign `resolved` as the reason for locking. Set to `false` to disable
+setLockReason: false
+
+# Limit to only `issues` or `pulls`
+only: issues
+
+# Optionally, specify configuration settings just for `issues` or `pulls`
+# issues:
+#   exemptLabels:
+#     - help-wanted
+#   lockLabel: outdated
+
+# pulls:
+#   daysUntilLock: 30
+
+# Repository to extend settings from
+# _extends: repo